[czj]

Hi Yusuke, and thank you for keeping this client so close to upstream Playwright!

Route and ScreenshotUtils require mime/types at the top of their files, and since channel_owner.rb loads every channel owner, each require 'playwright' loads the whole MIME database. Yet it is only consulted in two places: Route#fulfill(path:), to guess the content type, and screenshot(path:) without an explicit type:. Most test suites never reach either, but they pay the load cost on every boot, and Rails apps that eager-load their test dependencies pay it in every process.

This PR moves the require into those two methods, as playwright.rb already does for playwright/web_socket_client. require is thread-safe and becomes a cheap lookup after the first call. I added a unit spec for ScreenshotUtils.determine_type (which had none) and one that checks, in a subprocess, that require 'playwright' no longer loads mime/types. That spec fails on main.

Measured with ruby -I lib -e "require 'playwright'" (no Bundler), Ruby 4.0.8 arm64, mime-types 3.7.0, median of 5 runs:

require 'playwright'	main	this branch
Wall time	173 ms	124 ms (−28%)
Allocated objects	214,866	80,194 (−63%)
Live objects after GC	69,539	45,104 (−35%)
ObjectSpace.memsize_of_all	5.1 MB	2.5 MB
RSS	30.5 MB	26.7 MB

The unit suite passes (36 examples, 2 pending as before), and so do request_fulfill_spec, route_spec and screenshot_spec against playwright-core 1.64.0 on Chromium (41 examples). I also checked by hand that route.fulfill(path: 'empty.html') still answers with text/html.

One thing to be aware of: code that used MIME::Types without requiring it, relying on Playwright to load it, would now need its own require 'mime/types'.

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